java combine two linkedlist

问题

I have a question for combining two linkedlist. Basically, I want to append one linkedlist to the other linkedlist.

Here is my solution. Is there a more efficient way to do it without looping the first linkedlist? Any suggestion would be appreciated.

    static Node connect(LinkedList list1, LinkedList list2) {
    Node original = list1.first;
    Node previous = null;
    Node current = list1.first;
    while (current != null) {
        previous = current;
        current = current.next;
    }
    previous.next = list2.first;
    return original;
}

回答1:

Use list1.addAll(list2) to append list2 at the end of list1.

回答2:

For linked lists, linkedList.addAll(otherlist) seems to be a very poor choice.

the java api version of linkedList.addAll begins:

public boolean addAll(int index, Collection<? extends E> c) {
    checkPositionIndex(index);
    Object[] a = c.toArray();

so even when you have 2 linked lists, the second one gets converted to an array, then re-constituted into individual elements. This is worse than just merging 2 arrays.

回答3:

I guess this is your own linked list implementation? With only a pointer to next element, the only way to append at the end is to walk all the elements of the first list.

However, you could store a pointer to the last element to make this operation run in constant time (just remember to update the last element of the new list to be the last element of the added list).

回答4:

The best way is to append the second list to the first list.

1. Create a Node Class.

2. Create New LinkedList Class.

public class LinkedList<T> {

        public Node<T> head = null;

        public LinkedList() {}

        public void addNode(T data){
            if(head == null) {
                head = new Node<T>(data);
            } else {
                Node<T> curr = head;
                while(curr.getNext() != null) {
                    curr = curr.getNext();
                }
                curr.setNext(new Node<T>(data));
            }
        }

        public void appendList(LinkedList<T> linkedList) {
            if(linkedList.head == null) {
                return;
            } else {
                Node<T> curr = linkedList.head;
                while(curr != null) {
                    addNode((T) curr.getData());
                    curr = curr.getNext();
                }
            }
        }
}

3. In the Main function or whereever you want this append to happen, do it like this.

LinkedList<Integer> n = new LinkedListNode().new LinkedList<Integer>();
    n.addNode(23);
    n.addNode(41);
LinkedList<Integer> n1 = new LinkedListNode().new LinkedList<Integer>();
    n1.addNode(50);
    n1.addNode(34);
n.appendList(n1);

I like doing this way so that there isn't any need for you to pass both these and loop again in the first LinkedList.

Hope that helps

来源：https://stackoverflow.com/questions/6295277/java-combine-two-linkedlist